1. Field of the Invention
The present invention relates to a display apparatus for a vehicle, in particular, a head-up display apparatus having a reflection mirror for allowing a vehicle driver to see both a forward view through a windshield and a reflected image projected from a display source superimposed thereon, and the head-up display apparatus having a reflection mirror formed for compensating a distortion of the displayed image caused by non-planarity of the windshield.
2. Description of the Related Art
Nowadays, a projector referred to as a head-up display apparatus (HUD) is installed in some vehicles for improving visibility of a vehicle driver.
FIG. 4A shows a schematic view for explaining reflections of light beams at a windshield 3 and at an aspherical mirror 4 projected toward a center of an eye range IR (view point). FIG. 4B shows reflecting points on a reflecting surface of the aspherical mirror.
As shown in FIG. 4A, a conventional HUD includes: a reflection mirror 4 disposed under an instrument panel 1 of a vehicle; and a display source 5 such as a Field Emission Display, an Electroluminescent Display, or an Liquid Crystal Display with backlighting. An image displayed on the display source 5 is reflected by the reflection mirror 4, projected on a projection area E of the windshield 3 through an opening (not shown) on the instrument panel 1. The projected image is superimposed on a forward view through the windshield.
The eye range IR includes an eye point IU corresponding to an upper limit of the eye range IR, an eye point IL corresponding to a lower limit of the eye range, and an eye point IM disposed on a middle of the eye range IR. An aspherical mirror is often used as the reflecting mirror 4 for compensating a distortion caused by non-planarity of the windshield 3.
As shown in FIGS. 4A and 4B, the reflecting surface of the reflecting mirror 4 is so designed as to compensate the image reflected on reflecting points A1, B1, C1 positioned on the reflecting mirror 4 corresponding to projecting points A0, B0, C0 positioned on the windshield 3. The reflecting points A1, B1, C1 correspond to an upper, a middle, and a lower parts of the display source 5 respectively.
The head-up display apparatus includes an image adjustment mechanism to the eye range. The image is so adjusted that an angle of depression from the eye point is constant throughout the adjustment.
An applicant of the present invention discloses a head-up display apparatus for adjusting the image to the eye point precisely in Japanese Published Patent Application No. 2003-39981.
A large sized head-up display apparatus is used for a night vision or the like. Usually, such a large-sized head-up display apparatus is retractable. A foldable reflecting mirror is disclosed in Japanese Published Patent Application No. H09-315182.
Further, Japanese Published Patent Application No. 2004-196228 discloses a head-up display apparatus having a quickly openable and closable reflection mirror, a reflection angle of which is easily adjustable.
However, there is a problem that the head-up display apparatus having an angle adjustment mechanism is large-sized because the reflection mirror and the display source should be movable.
Further, as shown in FIGS. 5A to 5C, when a cross point of optical axes toward the eye points of the eye range is designed to be positioned in the vicinity of the reflecting surface, the projecting points on the windshield are separated. Therefore, it is difficult to compensate the distortion.
As shown in FIGS. 5A to 5C, with a reflection mirror 4 rotated about a rotating shaft 121 disposed at the vertical center thereof, when the cross point of optical axes LU, LM, LL respectively corresponding to eye points IU, IM, IL of the eye range is positioned in the vicinity of the center of a reflecting surface 4a of the reflection mirror 4, reflecting points D2, E2, F2 on the reflecting surface 4a are concentrated at the same position, however, projecting points D0, E0, F0 on the windshield 3 are separated from each other.
Accordingly, since the projecting points are moved by the adjustment of the eye range IR, the distortion of the image caused by the non-planarity of the windshield 3 is hard to be compensated even with the aspherical mirror 4.
The head-up display apparatus disclosed in the Japanese Published Patent Application No. 2004-196228 is also large-sized because the angle adjustment needs a widely opened reflection mirror. That is because a mechanism for opening and closing the reflection mirror is cooperated with the angle adjustment mechanism, and the angle adjustment mechanism cannot work until the mirror is opened at a specific angle.
There is another problem in the head-up display apparatus having a stopper 141 used for fine adjustment of the reflection mirror. As shown in FIGS. 8A and 8B, the head-up display apparatus includes the reflection mirror 4, a rotating shaft 6 rotated with the reflection mirror 4, a conventional angle adjustment mechanism for rotating the rotating shaft 6, and the stopper 141 for fine adjustment of an angle of the reflection mirror 4.
The stopper 141 cannot be moved together with the reflection mirror 4. Accordingly, when finely adjusting the reflection mirror 4, firstly, the angle adjustment mechanism rotates the reflection mirror 4 in a direction X, then, the stopper 141 is moved in a direction Z, and then the angle adjustment mechanism rotates the reflection mirror 4 in a direction Y to bring the reflection mirror 4 into contact with the stopper 141. Thus, a reciprocating motion of the reflection mirror 4 is needed for the fine adjustment thereof.
Accordingly, an object of the present invention is to provide a small-sized head-up display apparatus that projects an image without distortion, and allows a position of the image and an angle of a reflection mirror to be easily adjusted.